What is the term for the fixed or removable ring, tube, or lining around a chimney connector?

The term "thimble" refers to a specific component in chimney systems that serves to provide a fixed or removable connection for a chimney connector. This connection facilitates the safe passage of flue gases from the appliance to the chimney. The thimble is designed to fit around the connector, offering stability and a proper seal, which helps to prevent leaks of combustion gases into the living space.

In contrast, a flue is the internal passageway within a chimney that allows the exhaust gases to exit safely to the outside environment. The insert typically refers to a type of fireplace or stove designed to be installed within an existing structure, while the shell could describe the outer casing of the chimney itself, but does not specifically represent the connection component. Thus, the use of "thimble" is more precise in describing this particular part of the chimney system.